The present disclosure relates to transport refrigeration units and, more particularly, to evaporator defrosting and associated control logic.
Traditional refrigerated cargo trucks or refrigerated tractor trailers, such as those utilized to transport cargo via sea, rail, or road, is a truck, trailer or cargo container, generally defining a cargo compartment, and modified to include a refrigeration system located at one end of the truck, trailer, or cargo container. Refrigeration systems typically include a compressor, a condenser, an expansion valve, and an evaporator serially connected by refrigerant lines in a closed refrigerant circuit in accord with known refrigerant vapor compression cycles. A power unit, such as a combustion engine, drives the compressor of the refrigeration unit, and may be diesel powered, natural gas powered, or other type of engine. In many tractor trailer transport refrigeration systems, the compressor is driven by the engine shaft either through a belt drive or by a mechanical shaft-to-shaft link In other systems, the engine drives a generator that generates electrical power, which in-turn drives the compressor.
Evaporators of the refrigeration units are used during the refrigeration process to maintain appropriate temperatures within the cargo compartment. During the cooling cycle, humidity in the air within the cargo compartment may collect on the evaporator in the form of ice. Continued buildup of ice reduces the evaporator efficiency, thus a defrost cycle may be initiated by the unit to remove the ice. Manufacturers and operators of fleets of refrigerated trucks, trailers and/or cargo containers desire to maximize operational efficiency of the entire operation cycle(s) of the refrigeration system. One area of improvement may be made with respect to the defrosting capability of the refrigeration system.